1. Field of the Invention
The present invention relates to a colored composition to be used for the manufacture of a color filter to be used in a color liquid crystal display device, a color image pickup device, etc., to a color filter and to the manufacturing method thereof.
2. Description of the Related Art
A filter segment or a black matrix, which constitutes a color filter for use in a color liquid crystal display device, a color image pickup device, etc., can be manufactured by a process including coating a substrate such as a glass substrate with a photosensitive material to form a photosensitive layer, drying the layer to remove any excess solvent therefrom, and irradiating the layer with an active energy beam by the application of proximity exposure (ultraviolet source exposure) through a photomask designed for forming pixels, thereby curing the layer (negative type) or increasing the alkali-solubility of the layer (positive type) to create easily dissoluble portions, which are subsequently selectively dissolved by making use of an alkaline solution, etc. This process is repeated for each color, thereby manufacturing a color filter.
In recent years, a color liquid crystal display device is widely employed in liquid crystal color televisions, in car navigation, and in liquid crystal display device-integrated notebook-sized personal computers, thus representing a large market. Further, by taking advantage of the characteristics of color liquid crystal display devices, such as energy-saving and space-saving, liquid crystal display devices are now propagated as a monitoring device for desktop personal computers and televisions. Additionally, as liquid crystal display devices have gained much market penetration, there is an increasing demand for improvements in the color reproduction characteristics.
Further, it has been generally practiced to interpose a black matrix between the filter segments constituting each pixel of the color filter in order to improve the color contrast. However, from the viewpoints of overcoming environmental problems, lowering the reflection of the black matrix and reducing the manufacturing cost, the employment of a resinous black matrix containing a light-shielding pigment dispersed in a resin has now attracted attention as a possible candidate to replace the conventional metallic chrome black matrix. This resinous black matrix, however, is accompanied with a problem that the light-shielding property (optical concentration) thereof is lower than that of the metallic chrome black matrix.
In order to improve the color reproduction characteristics of the color filter and also to improve the light-shielding property of the resinous black matrix, it is necessary to increase the content of the pigment in a photosensitive colored composition constituting the black matrix or to increase the thickness of the black matrix. However, according to the conventional technique wherein proximity exposure (ultraviolet source exposure) is employed as an active energy source, when the content of the pigment is increased, various problems are caused to arise, such as a lowering of the sensitivity, a deterioration in the developing property, a deterioration in the resolving property, etc. On the other hand, when the film thickness of the resinous black matrix is increased, it may become difficult for the exposure light to reach the bottom portion of the film, raising various problems such as a deterioration in not only the linearity but also the sectional configuration in the filter segment and the black matrix, etc.
In order to overcome these problems, it is required to enhance the sensitivity of the photosensitive colored composition, as is suggested in JP-A 2003-156842, wherein (1) the addition of a reactive double bond to a resin; (2) the selection or content increase of a photo-polymerization initiator or of a photosensitizer; and (3) the selection or content increase of a monomer are disclosed.
On the other hand, due to a trend in recent years to further increase the size of display devices equipped with a color filter, the size of the photomask for forming the filter segment and the black matrix is also inevitably required to be made larger, thereby leading to an increase in manufacturing cost.
Meanwhile, JP-A 9-269410 describes, as means for exposure processing, the employment of an active energy beam such as ultraviolet ray, excimer laser beam, X-ray, gamma ray, electron beam, etc. which is designed to be irradiated at a dosage of 30-2000 mJ/cm2. Although concept of curing a colored composition through the irradiation of excimer laser beam as an active energy beam source is known, as described in the aforementioned Publication, there is no publication disclosing a method for creating a color filter by making use of an excimer laser. Likewise, no one has succeeded as yet in developing a colored composition which is compatible with an excimer laser and can be put into practical use.
In the case of the proximity exposure method (ultraviolet source exposure method) which has been generally employed, in order to enable a large substrate to be treated, a photomask which is expensive and large in size so as to match the size of the substrate is required to be employed. Therefore, there is a problem of how to reduce the manufacturing cost of the photomask.
Further, when the content of a coloring matter such as pigment is increased so as to improve the color reproduction characteristics and light-shielding properties of a color filter, the curing of the photosensitive colored composition may be obstructed. In order to overcome this problem, it is necessary to increase the content of a photo-polymerization initiator or to additionally incorporate a photosensitizer. However, since the photo-polymerization initiator is very expensive, the problem is how to reduce the quantity of the photo-polymerization initiator to lower the manufacturing cost of the color filter.
Additionally, the employment of a different kind of photo-polymerization initiator for each color of the photosensitive colored composition is disadvantageous in terms of delivery as well as in the embodiment of manufacturing cost.